Control circuit for solenoid valve

ABSTRACT

A solenoid valve for a water purification system. The solenoid valve contains a fluid valve which can move between an opened position and a closed position, and a coil which moves the valve to the open position when a first voltage is supplied to the coil and maintains the valve in the open position as a second voltage is supplied to the coil. The coil is coupled to a control circuit which initially supplies the first voltage to the coil when the valve is to be opened, and then reduces the first voltage to the second voltage after the valve is in the open position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solenoid valve for a waterpurification system.

2. Description of Related Art

Water purification systems typically include a pump that pumpscontaminated water through a filter unit. The filter may contain areverse osmosis membrane which removes impurities in the water. Thewater is then stored within a tank and subsequently removed by the enduser. Water purification systems range in size from large industrialunits to smaller systems that can be installed under the sink of a home.

Residential water purification units typically have a valve thatcontrols the flow of water between the pump and a municipal watersource. To more fully automate the purification unit, the valves maycontain solenoids which are controlled by a control circuit. The valvestypically move into an open position when the control circuit providespower to the solenoid. Most solenoid operated valves require arelatively large amount of current to move the valves from the closedposition to the open position. The large current is typically needed toovercome the fluid back pressure exerted on the valve, and the internalair gap within the valve and flux gap. Once the valve is opened, thesolenoid does not require the large initial current needed to open thevalve. The continual supply of excessive power to the valve, mayoverheat the solenoid and draw in an unnecessary amount of power. Theheat may cause the solenoid to fail, thereby reducing the life andreliability of the valve unit. Additionally, the excessive use of powercreates a valve that is costly to operate.

The control circuit of the valve is typically powered by the sametransformer that powers the motor of the pump. When the pump is turnedon, the motor requires a gradually increasing amount of current tocorrelate with the increasing speed of the pump unit and the backpressure that is generated by the pump. In a typical water purificationsystem, the solenoid valve and pump unit are activated simultaneously,so that municipal water is pumped to the filter unit. The transformermust pull in an increasing amount of power during the initial state ofthe pumping cycle to accommodate the constant current requirement of thesolenoid valve and the ramping current requirement of the pump motor.The transformer must therefore be built to accommodate the maximumcurrent requirements of both devices. It would be desirable to have asolenoid valve which only requires an initial large current to open thevalve and then draws a lower amount of current to maintain the valve inthe open position. It would also be desirable to have a solenoid valvethat has a decreasing current load requirement that matches theincreasing load requirement of the pump motor, so that the powerprovided by the transformer is approximately a constant value during theentire pumping cycle of the system. Residential water purificationsystems typically have used an AC powered solenoid valve that is drivenby the same transformer that supplies power to the systems otherelectric al components.

AC powered transformers becomes objectionably noisy if the armature isnot in full contact with the core of the solenoid. The noise is createdby the variable field strength form the alternating current rocking thearmature. It would therefore be desirable to have a control circuit thateliminates the risk of noise by providing a DC holding current.

SUMMARY OF THE INVENTION

The present invention is a solenoid valve for a water purificationsystem. The solenoid valve contains a fluid valve which can move betweenan opened position and a closed position, and a coil which moves thevalve to the opened position when a first voltage is supplied to thecoil and maintains the valve in the open position as a second voltage issupplied to the coil. The coil is coupled to a control circuit whichinitially supplies the first voltage to the coil when the valve is to beopened, and then reduces the first voltage to the second voltage afterthe valve is in the open position.

The valve control circuit may be connected to a tank control circuit,which is coupled to a transformer and a water level sensor within astorage tank. The storage tank is connected to a reverse osmosismembrane that purifies water that is pumped through the system by a pumpunit. The tank control circuit is constructed to provide power from thetransformer to the pump and solenoid valve when the water within thetank reaches a first level, and terminate power to the pump and valvewhen the water within the tank rises to a second level. The tank controlcircuit includes a latching scheme which prevents oscillation of thepower switches about the first and second levels of the tank.

The solenoid valve has a gradually decreasing current load whichpreferably matches a gradually increasing current load of the pump unit,so that the transformer provides an approximately constant level ofpower during the entire pumping cycle of the system.

Therefore, it is an object of the present invention to provide asolenoid valve which initially opens with a first voltage and ismaintained in the open position by a lower second voltage.

It is also an object of the present invention to provide a waterpurification system that draws an approximately constant level of powerduring the entire pumping cycle.

It is also an object of the present invention to provide a solenoidvalve that is energy efficient and does not dissipate a large amount ofheat.

It is also an object of the present invention to provide a controlcircuit that can control power to both a pump and a solenoid valve.

It is also an object of the present invention to provide a controlcircuit that eliminates the possibility of noise and vibration from thesolenoid valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become morereadily apparent to those ordinarily skilled in the art after reviewingthe following detailed description and accompanying drawings, wherein:

FIG. 1 is a schematic of a solenoid valve circuit of the presentinvention;

FIG. 2 is a graph showing the output voltage of a valve control circuitas a function of time;

FIG. 3 is a schematic of the solenoid valve of FIG. 1 in a waterpurification system;

FIG. 4 is a graph showing the current load requirements of a pump motorand solenoid valve of the water purification system of FIG. 3;

FIG. 5 is a schematic of the tank control circuit of FIG. 2;

FIG. 6 is a side view of a housing for the solenoid valve.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings more particularly by reference numbers, FIG. 1shows a circuit for a solenoid valve 10 of the present invention. Thesolenoid valve 10 typically has a fluid valve 12 coupled to a coil 14.The valve 12 is adapted to move between an open position and a closedposition. The valve moves from the closed position to the open positionwhen a voltage is applied to the coil 14. The solenoid valve may alsohave a spring that biases the valve to the closed position.

The coil 14 is connected to the output pins 16 of a valve controlcircuit 18 which controls the power supplied to the coil 14. The controlcircuit 18 also has a pair of input pins 20 that are typically connectedto a source of AC power. The AC power is rectified to DC power byrectifier 22.

The control circuit 18 has a pnp transistor 24 that has an emitter E1connected to a power supply line 26 and a collector C1 coupled to thecoil 14. The emitter E1 is in parallel with resistor R1. The collectorC1 is coupled to resistor R2. The resistors R1 and R2 are both connectedto the base B1 of the transistor 24. The transistor 24 is also inparallel with resistors R3 and R4 which are both connected to the powersupply line 26 and the coil 14.

The control circuit 18 may have a first capacitor C1 which is inparallel with the rectifier 22. The circuit also has a second capacitorC2 which is coupled to the base B1 of the transistor 24. Between thesecond capacitor C2 and the power supply line 26 is a diode D1.

In operation, the AC voltage source supplies a source voltage which isrectified and provide to the control circuit 18 as a DC voltage Vr. Thecurrent from the power source initially flows through the pnp transistor24, which is operating above the saturation point of the device 24. Thecurrent flow through the transistor provides a first voltage V1 at thecoil 14 that is approximately equal to the rectified source voltage Vr.The application of the first voltage V1 to the coil 14 moves the fluidvalve 12 into the open position. The first voltage V1 is typically greatenough to overcome any resistive forces on the valve 12. For example,the torque created by the coil 14 is typically greater than the fluidback pressure that is exerted on the fluid valve 12. As power is appliedto the coil, the second capacitor C2 is drawing current and beingcharged. The flow of current to the second capacitor C2 maintains thebiasing current B1 below the transition level of the transistor, so thatthe pnp transistor stays on while the second capacitor C2 is beingcharged.

As the second capacitor C2 charges up, more current flows into the baseB1, thereby reducing the current that flows across the transistor 24 andinto the coil 14. When the second capacitor C2 becomes completelycharged, the capacitor C2 becomes an open circuit to the DC powersupplied from the rectifier 22. When the capacitor C2 reaches the fullycharged state, the current at the base B1 reaches a level that turns thetransistor off. The rectified source voltage Vr is then applied acrossthe resistors R3 and R4. The resistors R3 and R4 are typically an orderof magnitude larger than the resistive value of R1. As shown by thegraph in FIG. 2, the resistors R3 and R4 reduce the voltage applied tothe coil 14 to a second voltage level V2. The second voltage V2 is largeenough to maintain the fluid valve 12 in the open position.

As shown in FIG. 3, the solenoid valve 10 may be used in a waterpurification system. The purification system has a pump 30 which pumpswater through a reverse osmosis membrane 32 from an external source ofwater. The purified water is typically stored in a storage tank 34. Thestorage tank 34 contains a sensor systems 36 that senses when the waterwithin the storage tank 34 reaches a first predetermined level and asecond predetermined level. The sensor system 36 may include floatingcontacts, pressure transducers or any other means for sensing the levelof water within the tank.

The tank sensors 36 are connected to a tank control circuit 38. The tankcontrol circuit 38 is connected to a transformer 40 and a motor 42 thatdrives the pump 30. The tank control circuit 38 functions as a switchbetween the transformer 40, and the solenoid valve 10 and motor 42. Thecontrol circuit 38 is constructed so that power is supplied to the motor42 and valve 10 when the tank water is at the first level, and power isnot supplied to the motor 42 and valve 10 when the tank water level isat the second level.

In operation, the tank control circuit 38 supplies power to the solenoidvalve 10 and motor 42 to open the valve 10 and drive the pump 30,respectively. Water is pumped through the membrane until the waterwithin the storage tank reaches the second predetermined level. The tankcontrol circuit 38 then terminates the power to the motor 42 andsolenoid valve 10, respectively.

As shown by the graph in FIG. 4, the capacitors and resistors of thevalve 10 control circuit 38 are typically selected so that thedecreasing current requirements of the solenoid valve 10 correspond tothe increasing current requirements of the pump 30. This matchingcurrent requirement produces a purification system which draws arelatively constant supply of power through the transformer during theentire water pumping cycle of the system.

FIG. 5 shows a preferred embodiment of the tank control circuit 38. Thecircuit 38 has output pins PO1 and PO2 connected to the solenoid valve10 and motor 42, and power input pins PI1 and PI2 connected to theoutput of the transformer 40. The circuit 38 also has sensor pins S1 andSh that are connected to the sensor system 36 of the storage tank 34.

The control circuit 38 contains a npn transistor 50 which has an emitterE2 connected to a power supply line of the transformer output throughresistor R5 and to a transformer reference line through capacitor C3, acollector C2 that is coupled to the gate of a triac 52 through diode D2and resistor R6, and a base B2 that is connected to the power supplyline through capacitor C4 and diode D3, and also coupled to a first nodeof the triac 52 through capacitors C5 and C6. The circuit 38 alsocontains capacitor C7 which is coupled to the gate of the triac 52.

In operation, when the water within the storage tank falls to the firstlevel, the sense pin S1 becomes coupled to the transformer 40, so thatthe transistor biasing current flows through capacitor C4. The biasingcurrent switches the transistor 50 so that current flows throughresistor R6 and into the gate of the triac 52. The triac 52 is thenbiased so that current can flow through the device 52 and into the motor42 and solenoid valve 10. The capacitor C7 provides energy to the gateof the triac 52 during the negative half cycle of the AC power.

The current from the triac 52 also flows back into the base B2, so thata biasing current is maintained at the transistor 50, even when thesense pin S1 becomes decoupled from the transformer 40 and current nolonger flows through capacitor C4. This latching scheme allows the pump30 to continue pumping even when the water rises above the firstpredetermined level in the tank 34. Such a system prevents poweroscillation about the first water level.

Power is supplied to the motor 42 and valve 10 until the water levelwithin the storage tank 34 reaches the second level, at which point thesense pin Sh is coupled to ground. The output of the triac 52 alsobecomes coupled to ground, which drains the biasing current and turnsoff the transistor 50. Turning off the transistor 50 eliminates thebiasing current to the triac 52, which turns the triac 52 off andterminates power to the motor 42 and solenoid 10.

FIG. 6 shows a preferred embodiment of a solenoid valve unit enclosed bya housing 60 that has a first compartment 62 and a second compartment64. The first compartment 62 typically contains the fluid valve 12 andcoil 14 of the solenoid valve unit. The second compartment 64 typicallycontains the control circuit 38 for the valve unit. The housing 60 has apassage 66 which allows wires to connect the coil 14 in the firstcompartment 62 to the control circuit 18 in the second compartment 64.The compartments are separated by an air channel 68. The air channel 68is typically thin, so that the mode of heat transfer between thecompartments 62 and 64 is primarily through conduction. The air channel68 provides an insulative barrier between the compartments, so that theheat dissipation of the coil 14 is not readily transferred to thecontrol circuit 18.

What is thus provided is a energy efficient solenoid valve 10 which canbe used to control the flow of water into the pump 30 of a waterpurification system so that a relatively constant supply of power ispulled by the system during a water purification cycle.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

What is claimed is:
 1. A solenoid valve, comprising:a valve adapted tomove between a first position and a second position; a solenoid thatmoves said valve from said first position to said second position when afirst voltage is applied to said solenoid, and maintains said valve insaid second position when a second voltage is applied to said solenoid,wherein said first voltage is greater than said second voltage; asolenoid circuit that initially applies said first voltage to saidsolenoid to move said valve to said second position and thensubsequently applies said second voltage to said solenoid to maintainsaid valve in said second position, said second voltage being applied tosaid solenoid a predetermined time interval after application of saidfirst voltage to said solenoid, said solenoid circuit contains a Voltagedivider circuit connected to said solenoid, a transistor connected tosaid voltage divider circuit and said solenoid, a capacitor connected tosaid transistor, and a single source of power connected to said voltagedivider circuit, said transistor and said capacitor, such that saidcapacitor is initially charged and said transistor is in an active stateso that current from the power source by-passes said voltage divider andsaid first voltage is applied to said solenoid, and said capacitorbecomes charged and said transistor is in an inactive state to allowcurrent to flow through said voltage divider circuit so that said secondvoltage is applied to said solenoid, wherein said predetermined timeinterval is dependent on a time constant of said capacitor.
 2. Thesolenoid valve as recited in claim 1, further comprising a housing thathas a U-shaped wall with a first portion separated from a second portionby an air channel, wherein said first portion partially defines a firstcompartment that contains said valve and said solenoid, and said secondportion partially defines a second compartment that contains saidsolenoid circuit.